Implantable medical devices (IMDs) include devices designed to be implanted into a patient. Some examples of these devices include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization therapy devices (CRTs), and devices that include a combination of such capabilities. The devices can be used to treat patients using electrical or other therapy or to aid a physician or caregiver in patient diagnosis through internal monitoring of a patient's condition. The devices may include one or more electrodes in communication with one or more sense amplifiers to monitor electrical heart activity within a patient, and often include one or more sensors to monitor one or more other internal patient parameters. Other examples of implantable medical devices include implantable diagnostic devices, implantable drug delivery systems, or implantable devices with neural stimulation capability.
Additionally, some IMDs detect events by monitoring electrical heart activity signals. Some IMDs derive measurements of hemodynamic parameters related to chamber filling and contractions from electrical signals provided by sensors. Sometimes patients who receive IMDs have experienced heart failure (HF) decompensation or other events associated with worsening HF. Some patients have experienced repeated HF decompensations. Symptoms associated with worsening HF include pulmonary and/or peripheral edema, dilated cardiomyopathy, or ventricular dilation. Early attention to signs and symptoms of HF decompensation is needed for the health of the patient and allows early initiation of treatment.